Defoamer formulations are widely used in industrial applications to control foam produced by mechanical agitation or shearing of fluids. They may be comprised of low viscosity oils, polyols and low foam surfactants. Commercial defoamer formulations may also contain hydrophobic particles to break the foam, by adsorbing to the air/liquid interface and changing the contact angle.
Defoamer compositions containing hydrophobic particulates (such as hydrophobically modified silica or fatty acid amides, e.g. behenamide and diamides) often require complex processing, whereby the waxy material has to be melted and then cooled to produce solid in the oil phase with the appropriate particle size distribution. A major drawback of these defoamers is the separation of the particulates from the formulation, which may result in the particulates depositing in an unwanted manner. In particular, there may end up being unwanted deposits on equipment surfaces or blockages of injection lines or filters. This may necessitate costly clean up operations.
Silicone antifoam/defoamer formulations are an important group of foam control systems; these include polydimethylsiloxane/silica dispersions and the like. They are commercially available as O/W (oil in water) or W/O (water in oil) emulsions. They are primarily used to suppress the production of foam in applications such as laundry detergents, pulp and paper (particulate stabilized foams), mineral processing, food processing (proteinous foams), agrochemicals and oilfield applications. Although the use of silicone antifoams is widespread in oilfield applications, there are instances where their use may be prohibitive owing to the potential risk of downstream production problems. A particular area of concern is the refining of petroleum where the presence of silicone antifoams may cause catalyst poisoning or contamination of products such as fuels. As a consequence of these problems their use has been restricted in oilfield production facilities in recent years. Silicone antifoams have additional drawbacks such as the deterioration in their efficiency in highly alkaline media as a result of hydrolysis, which is relevant in applications such as pulp and paper processing.
Defoamer formulations that are free of silicone are also used, but they also have practical limitations. They are either O/W or W/O emulsions comprised of low foam surfactants (e.g. EO/PO block copolymers), hydrophobic particles, mineral oils, paraffinic (e.g. white oils), vegetable and synthetic oils (e.g. esters). They may suffer from instability at low or high temperature (creaming) and may form thick pastes or creams which are difficult to pump. Compositions based on low foam nonionic surfactants rely on the cloud point of the amphiphiles in aqueous solution for their mode of action. The surfactant is insoluble above its cloud point and behaves as an antifoam particle. Below the cloud point the surfactants are soluble in the aqueous media and therefore are considered to be non-depositing. This is described in, for example, U.S. Pat. Nos. 4,946,625 and 4,960,540.
Foams generated in oilfield production lines are complex dispersions consisting of solid particulates (asphaltenes, paraffin waxes, scales, e.g. alkali metal carbonates or iron sulfide, rust and sands), surface active components (natural resins, napthenate soaps, corrosion inhibitors, proteins), brine and hydrocarbons. The complexity of the foams makes it is difficult to control the volume produced by the release of volatile hydrocarbons in the separators. Therefore more effective defoamer systems are needed.